you meant to say that in DNA test we check bands if the band find to be similar in two beings than it is said to be related one's.
well, how can we distinguish that he is father and he/she is his off-spring
thanks alot

this is quite complicated. but over all the simple is
you need to determine the codes. this is very complex, really(because i'm new in the practical activies in the lab).
you can use some recomended software for make it. hm.. you may use bioinformatic for its data base.

the simple is the Mendel Theory. you will get the book or the reference(s) easily.
hey.. if i do not wrong, there should a topic in this forum at "genetic".

Mr.Smoke wrote:you meant to say that in DNA test we check bands if the band find to be similar in two beings than it is said to be related one's.well, how can we distinguish that he is father and he/she is his off-springthanks alot

As I told you, by the bands. Offsprings got genes from half from their mother and half from their father. It means that thru DNA test, offsrings will show bands that owned by their parents.

For instance, a kid named Jenny asked her mother who her father is. Unfortunately Jenny's mother cannot tell because she slept with three men named John, Smith, and Barry. Thru DNA test, Jenny shows more bands similar to John rather than Smith and Barry. However, John rejects to be her father, otherwise Barry claims he is her father because he takes care of her since she was a baby. In this case, the biological father is absolutely John because she brings John's genes shown by DNA test.